This invention relates to a method and an apparatus for detecting a target objective based on radio waves reflected from the target objective in response to transmission of the radio waves, and also relates to a method and an apparatus for discriminating a type of the detected target objective.
The FMCW type radar apparatus using millimeter radio waves (hereinafter, referred to as “FMCW radar”) is known as one of conventional radar apparatuses used for measuring and controlling a distance between traveling automotive vehicles.
The FMCW radar uses radio waves which are frequency modulated so as to have an ascending section in which the frequency gradually increases and a descending section in which the frequency gradually decreases. In each of the ascending section and the descending section, a signal component where the signal intensity becomes a peak (hereinafter, referred to as “peak frequency component”) is extracted based on a beat signal obtained by mixing transmitted and received radio wave signals. Then, a pair of peak frequency components originated from the same target objective is specified. And, the distance and a relative speed of the target objective are obtained based on the specified pair of peak frequency components.
In recent years, as considered in airbag controls performed in case of vehicle collision, it is preferable to optimize the control of an electronically controlled device according to the type of a target objective (e.g., large-sized vehicle/normal vehicle/non-vehicle objective). Regarding the method for discriminating the type of a detected target objective, it is for example possible to use a comparison between a signal intensity distribution of reflected radio waves relative to the scanning angle of a radio wave beam (which can de referred to as temporal variation of signal intensity) and a pre-stored model pattern, as disclosed in the Japanese Patent Application Laid-open No. 11-271441(1999). It is also possible to use a comparison between a signal intensity distribution of reflected radio waves relative to the frequency (which is a so-called frequency spectrum) and a pre-stored model pattern, as disclosed in the Japanese Patent Application Laid-open No. 5-27018(1993).
Furthermore, instead of using the radar, it is possible to use an image sensor to specify the shape of a target objective by processing the image data obtained from this image sensor and compare the specified shape with a pre-stored model pattern to accurately discriminate the type of a target objective.
However, according to each of the above-described methods, it is necessary to perform the comparison of the measured or detected data with a predetermined model pattern (so-called pattern matching). In other words, a huge amount of computation data must be processed. Furthermore, the signal intensity distribution has a tendency of momentarily changing depending on surrounding environments and others. Accordingly, preparing accurate model patterns is difficult.
Furthermore, from the standpoint of enhancing vehicle safety in a traveling condition, it is desirable to discriminate each detected objective between an automotive vehicle and a non-vehicle objective and also discriminate the type of each non-vehicle objective between a human and others.
However, in the case that the target objective is identified as being a non-vehicle objective, this target objective will be one of various kinds of objectives different in shape and size. The detected objective may be identical with a human in size or largeness or in signal intensity distribution. Accordingly, it is very difficult to accurately discriminate the difference between a human objective and a non-human objective according to the above-described conventional methods.
Furthermore, a human objective is different from an automotive vehicle or a roadside object in that the shape or contour is not constant and is possibly changing momentarily when observed. It means that many model patterns according to the position or attitude of a human objective will be necessary in discriminating the type of a detected target objective. Especially, according to the method requiring processing of image data obtained from an image sensor, the processing amount will greatly increase in accordance with the number of model patterns to be compared. The response will be worsened due to increase of processing amount. It is therefore not preferable to use this system for an automotive vehicle which requires speedy processing for avoiding collisions or accidents.